<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box {
            padding:  20px;
            background: palegoldenrod;
        }
    </style>
</head>
<body>
    <div id="box"></div>
    <button id="btn1">执行计算</button>
    <button id="btn2">改变背景</button>
    <script>
        var box = document.getElementById('box')
        var btn1 = document.getElementById('btn1')
        var btn2 = document.getElementById('btn2')
        var number = 99999
        var value = 0

        function calc (deadline) {
            while (number > 0 && deadline.timeRemaining() > 1) {
                value = Math.random() < 0.5 ? Math.random() : Math.random()
                console.log(value)
                number --
            }
            requestIdleCallback(calc)
        }

        btn1.onclick = function () {
            requestIdleCallback(calc)
        }

        btn2.onclick = function () {
            box.style.background = 'green'
        }
    </script>
</body>
</html>